A sensitive enzyme-linked immunosorbent assay (ELISA, EIA) was developed for the detection of delta antigen in serum treated with Tween 20. The serum delta antigen so derived was used in an ELISA for anti-delta. Both tests were specific and more sensitive than radioimmunoassay (RIA) when applied to testing parenteral drug abusers. It is concluded that the different sources of delta-antigen used may account for the different sensitivities noted, and that delta antigenaemia in acute infection may be more frequently detectable than was first thought, amounting to 71% of those with delta infection in this study and that these sera are a convenient alternative source of antigen.

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Hepatitis D virus (delta agent) markers were present in 111 (36%) of 308 intravenous drug abusers who were positive for hepatitis B surface antigen (HBsAg), 52 of these having hepatitis D virus antigenaemia. IgM antibody to hepatitis B core antigen (anti-HBc IgM) was present in 92 out of 95 subjects tested, indicating that hepatitis D virus and hepatitis B virus infections had been acquired simultaneously. Hepatitis D virus markers were present in three out of four patients with fulminant hepatitis, in seven of 11 (64%) with severe hepatitis, and in 80 of 223 (36%) with mild or moderate hepatitis compared with four of 29 (14%) of those who were asymptomatic. These proportional differences were significant (p <0 001). Hepatitis D virus markers were present in twice as many patients positive for anti-HBc IgM requiring admission to hospital with